Patched bug: enumeration_joint_ask gave wrong answers when the query variable overlaps the evidence.

Fixed: enumerate_joint_ask would raise KeyError on a combo of var values that didn't happen to be set. Though maybe this is too lenient, catching KeyError in ProbDist.__getitem__? (instead of in JointProbDist)

Agent.__init__ now takes a program parameter. A few more nonlocal-state-variable problems found and fixed. One agent program rewritten as a callable instance since it uses both state variables and abstract methods.

functions condprob and condsamp.

Added function event_values.

In BayesNet class, initialize instance variable evidence.

Simplified comments.

Added methods to the BayesNet class to needed for
enumeration_ask: variable_node, variables, variable_values.

Added Fig. 14.11a sprinkler network.

Completed/corrected prior_sample.

Implemented rejection_sampling.

The ProbDist normalize method now uses floating point division.

Implemented likelihood_weighting.

ProbDist constructor has an optional freqs (frequencies) argument.

Added function condsamp (samples from a CPT).

Additional doctest cases.